Name: Formation of New Species
Uploaded: 2019-07-19
Duration: 7 min 8 s
Description: New species are formed when their members are no longer able to reproduce with members of the parent species. See how new species are formed in this video.

Question

Explain stabilising, directional, and disruptive selection with examples.

Accepted Answer

The stabilising selection is called centripetal selection. It acts in the absence of large scale environmental changes for a long period. Mutations are eliminated. Thus, stabilising selection keeps a population genetically constant and maintains adaptiveness in natural populations.

Example: The birth weight of human babies provides an example influenced by stabilising selection. The optimum birth weight favoured by stabilising selection is 7.3 pounds. Newborn infants less than 5.5 pounds or more than 10 pounds have the highest mortality rate.

The directional selection is also known as Progressive selection. It produces a regular change within a population in one direction with respect to certain characteristics. This is due to change in the environment in a particular direction. It favours individuals that change in response to environmental change become best adapted to a new environment or ecological condition.

Example: The development of resistance to DDT or other insecticides by mosquitoes and houseflies is also an example of directional selection.

Disruptive selection occurs when a population previously adapted to a non-homogenous environment is subjected to divergent selection pressure in different parts of its area. It maintains balanced polymorphism in the population-based on frequency-dependent to the environment. It is a type of natural selection that tends to increase the amount of variance within the population.

Example: Shell patterns of limpets, marine molluscs present a continuous pattern, ranging from pure white to dark tan. They are either attached to white barnacles or tan coloured rocks. Limpets of intermediate shell patterns, being conspicuous are preyed on by predatory shorebirds, resulting in disruptive selection.

Explain stabilising, directional, and disruptive selection with examples.

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